Analysis of inhibitory mechanisms on Ca^<2+>-dependent K^+ channel influenced by exposure to a time-varying strong magnetic field.

我们测试了暴露于以下两个磁场（MF）对培养细胞的影响。(a)间隔3秒变化在0.07 ~ 1.7 T之间的时变MF。(b)极低频（ELF） ME（800高斯，50 Hz）。(1) ME (a)对HeLa细胞的影响：将正常培养基替换为高K^+培养基，激活细胞对K^+的摄取，增加细胞内Ca^<2+>浓度。发现膜渗透性Ca^<2+>螯合剂和Ca^<2+>依赖性K^+通道抑制剂可减少K^+摄取。暴露于MF部分抑制药物敏感性的K^+摄取，并完全抑制高K^+培养基中细胞内Ca^<2+>的增加。但Ca^<2+>离子载体的加入并不能恢复MF对K^+吸收的抑制。K^+通量的抑制可能与细胞表面电学性质的改变和Ca^<2+>内流或Ca^<2+>从细胞Ca^<2+>库释放的抑制有关。(2)通过FT-IR光谱分析ELF MF(b)对HeLa细胞的影响：在1500-1700 cm^<-1>区域的光谱分析中，MF使酰胺II模式（1540 cm-1）的吸光度降低，并使1600 cm^<-1>附近的吸光度瞬间增加。后一波段吸光度的增加表明游离羧基C=O对称振动的增加。这表明细胞膜的蛋白质结构和细胞表面的电学性质发生了变化。(3) ELF MF(a)对牛肾上腺嗜铬细胞的影响：我们测试了暴露于时变MF(a)对嗜铬细胞中缓激肽刺激的细胞内Ca^<2+>的短暂增加的影响。添加缓激肽可在数分钟内诱导细胞内Ca^<2+>升高。在无Ca^<2+>的培养基中，暴露于MF完全抑制细胞Ca^<2+>的增加。当最大磁通密度大于1.4 t时，对Ca^<2+>从细胞囊泡中释放有抑制作用。

We tested the effects of exposure to following two magnetic fields (MF) on cultured cells.(a) A time-varying MF changing between 0.07 and 1.7 T at an interval of 3 sec.(b) Extremely-low-frequency (ELF) ME (800 gauss, 50 Hz).(1) Effects of ME (a) on HeLa cells :K^+ uptake was activated and the intracellular Ca^<2+> concentration was increased by replacement of normal medium to high K^+ medium. A membrane-permeable Ca^<2+> chelating agent and Ca^<2+>-dependent K^+ channel inhibitors were found to reduce the K^+ uptake. Exposure to the MF partly inhibited the drug-sensitive K^+ uptake and completely suppressed the increase in intracellular Ca^<2+> in the high K^+ medium. But the inhibition of K^+ uptake by the MF was not restored by addition of Ca^<2+> ionophore. The suppression of K^+ fluxes could relate to a change in electric properties of cell surface and an inhibition of Ca^<2+> influx or Ca^<2+> release from cellular Ca^<2+> stores.(2) Analysis of ELF MF(b) effects on HeLa cells by FT-IR spectra :In analysis of the spectra of the 1500-1700 cm^<-1> region, absorbance of amide II mode (1540 cm-1)was decreased and a band about 1600 cm^<-1> was increased instantly by the MF.Increase in absorbance of the latter band reveals the increase on C=O symmetric vibration of free carboxyl. This results suggest changes in the protein structure of cell membrane and electric properties of cell surface.(3) Effects of ELF MF(a) on bovine adrenal chromaffin cells :We tested the effects of exposure to the time-varying MF(a) on transient increase in intracellular Ca^<2+> stimulated by bradykinin in chromaffin cells. Addition of bradykinin induced the increase in intracellular Ca^<2+> within few minutes.The exposure to the MF perfectly suppressed thc increase in cellular Ca^<2+> in Ca^<2+>-free medium. The inhibition occurred for 15 rain when the maximum magnetic flux density was more than 1.4 T.These results suggest that the exposure inhibits Ca^<2+> release from cellular vesicles.